The invention relates to optic neuritis.
Ethambutol is an essential drug in the management of mycobacterial infections. Ethambutol, a water-soluble and heat-stable compound, is active against nearly all strains of M. tuberculosis and M. kansasii as well as many strains of M. avium complex. It has no effect on other bacteria. Ethambutol suppresses the growth of most isoniazid-and streptomycin-resistant tubercle bacilli. This drug has few side effects, with the unfortunate exception of optic neuropathy. This can develop in up to 15% of patients taking ethambutol. Ethambutol can lead directly to a decline in visual acuity, the loss of the ability to differentiate red from green, the development of a central scotoma on visual field testing, or the development of concentric constriction of the visual field. In many cases, ethambutol-associated visual impairment is reversible. However, visual loss can be permanent in up to 3% of patients taking ethambutol.
The recent outbreaks of multidrug-resistant (MDR) TB pose an urgent public health problem and require rapid intervention. As a result of the increasing prevalence of drug-resistant TB in the United States, approaches to treatment of tuberculosis have changed. An initial four-drug regimen is now recommended for the treatment of TB. Treatment with the antibiotic, ethambutol, is favored as primary therapy for all newly diagnosed cases. Given the critical role played by ethambutol in the management of mycobacterial infections in both the general population and the AIDS-infected population, the potentially devastating visual loss that may result as a consequence of ethambutol therapy assumes great significance.
Although visual impairment and visual loss as a result of treatment with ethambutol and other agents has been well-documented, the mechanism by which the damage occurs has not been described.